In the past it has been customary to provide line switching devices which are effectively connectable in either direction to a source of alternating current supply, which supply would possess a ground or near ground conductor and one or more ungrounded conductors. The apparatuses of the prior art of which we are familiar incorporate relay arrangements that are selectively controlled in accordance with the direction of connection of the device to the alternating current supply. A typical form of equipment which meets this criteria is seen in the Rocha U.S. Pat. No. 2,870,380.
In mobile installations such as in mobile homes and in boats, difficulties can easily be encountered when an error is made in connecting the wires at the supply receptacle where the home or boat wishes to plug in. While it is customary to provide signalling devices such as buzzers or lights or the like to indicate errors in wiring, it becomes apparent that if there is an error in wiring, that short of rewiring the power supply receptacle, it becomes difficult for the average user to correct the situation. Also, and particularly in mobile situations, there is a possibility of an explosive gas mixture being present, which is particularly true in boats; further, approval of the authorities cannot be had with any device that could cause arcing, which would include manual switches and/or relays.
It has also been previously proposed in the past to provide additional protection to load circuits. To this end it has been customary to find ground-fault detectors wired into circuits, and these devices are principally designed to trip a circuit breaker whenever a dangerous leakage current develops as a result of faulty wiring. Such a device, however, protects only against one possible malfunction, which could threaten the safety of a human user or in the alternate, damage any equipment connected to the power source.